When a horse's hair goes white

The loss of hair pigment usually results from traumatic or inflammatory injuries, such as pressure from tack, too-tight or rubbing bandages, cuts, lacerations and even occasionally injections.
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Q: I’ve owned my mare for a little more than six months. She is in good health and is a pleasure to ride. She has a sleek chestnut coat and I take a lot of pride in keeping her looking good. From the time I first got her, however, I have noticed that she has white hairs across the bridge of her nose. A friend told me that this is most likely from an ill-fitting halter that someone put on her years ago. The white area is not large or particularly noticeable but I’d rather have the color return to that patch. Is there any way to get those hairs to be chestnut again or is the damage permanent?
Name withheld by request

In freeze branding, melanocytes are destroyed by extremely cold temperature but hair growth is unaffected leaving permanent white markings.

In freeze branding, melanocytes are destroyed by extremely cold temperature but hair growth is unaffected leaving permanent white markings.

 A: To understand how these white patches appear, it’s important to remember a few things about hair: Natural hair color is produced by pigment cells (melanocytes) within hair follicles that transfer pigment into the cells (keratinocytes) of the hair itself. Pigment is transferred to hair only when it is actively growing.

The loss of hair pigment, called leukotrichia, commonly occurs as a result of various traumatic and inflammatory injuries, such as pressure from tack, too-tight or rubbing bandages, cuts, lacerations and even occasionally injections. If an injury is severe enough, the hair follicle itself may be damaged, resulting in alopecia (lack of hair)---a bald area. 

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For your bookshelf:

Horse Owner's Veterinary Handbook
Storey's Barn Guide to Horse Health Care + First Aid
Horse Health Care: A Step-By-Step Photographic Guide to Mastering Over 100 Horsekeeping Skills
The Merck Veterinary Manual

Melanocytes are more susceptible to injury than is the hair itself; thus, milder injury can cause leukotrichia while hair growth remains. This is, in fact, the basis for freeze branding, in which the melanocytes are destroyed by extremely cold temperature but hair growth is unaffected. 

Essentially, the same process occurred on your mare’s nose. The ill-fitting halter caused inflammation and trauma that resulted in damage to the underlying pigment cells but not to the hair itself. Because pigmentation has not been restored in the hairs over many growth cycles, we can assume that the damage is permanent. Unfortunately, there is no treatment for this condition. Those white hairs are now a part of your mare’s unique markings. 

Linda A. Frank, MS, DVM, DACVD
University of Tennessee
Knoxville, Tennessee

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